1. Field of the Invention
The present invention relates to an electrothermal color-varying device, and more particularly such device of higher safety, capable of rapid heat generation in a heat generating member to a predetermined temperature by the application of a low voltage, thereby inducing a visible color change in a thermal color-varying layer, wherein the generated temperature is self-controlled to avoid danger resulting from overheating.
2. Related Background Art
There are already proposed, for example in the Japanese Laid-open Utility Model No. 62-137093 and the Japanese Laid-open Patent No. 62-201178, color-varying toys in which a color change in a color-varying layer is induced by current supply to an electrically energizable heat-generating member positioned behind said color-varying layer.
The heat-generating member in such proposals in a heater composed of a metal wiring capable of heat generation by current supply, such as tungsten, nickel or titanium, and an insulating ceramic material covering said metal wiring.
The heat-generating member employed in the above-mentioned conventional color-varying toys lacks the temperature self-controlling ability required for proper function in a desired temperature range, thereby involving danger of overheating and requiring therefore a temperature control switch or the like, and also necessitates insulation such as a ceramic covering in order to avoid danger of current leakage.